1. Field of the Invention
The present invention relates to rock boring machines, and in particular to a new rotary cutterhead construction for use on such a machine.
2. Description of the Prior Art
Rotary cutterheads have for some time been used in conjunction with various types of earth tunneling machines. Two examples of somewhat different tunneling machines are disclosed by U.S. Pat. No. 3,861,748, granted Jan. 21, 1975, to David T. Cass and by chapter 21 of the 1976 RETC Proceedings authored by Carlo Gorandori and published on or about June 14, 1976. The tunneling machines which are disclosed by these two publications include in basic form a frame structure which is composed of a cutterhead support and rearwardly projecting beam. A cutterhead carrying forwardly directed cutters is mounted on the cutterhead support for rotation about an axis corresponding to the longitudinal center of the tunnel being bored. The cutterhead support and usually at least the forward portion of the beam are encircled by a tubular shield having a diameter moderately less than the diameter of the tunnel being bored. A rear gripper assembly, which includes a set of gripper shoes for pressing laterally outwardly to bear against the side walls of the tunnel, is supported for sliding movement along the length of the beam. If the boring machine is to be used in relatively soft ground material, a rear shield may also be provided to encircle the rearwardly portion of the beam. The rear shield is provided with openings through which the rear gripper shoes may extend and retract.
Longitudinally disposed thrust rams interconnect the cutterhead support and the rear gripper assembly for lengthwise relative movement of the rear gripper assembly along the beam. Typical types of thrust rams are disclosed by U.S. Pat. No. 3,203,737 granted Aug. 31, 1975, to Richard J. Robbins, Douglas F. Winberg and John Galgoczy, and by U.S. Pat. No. 3,861,748 granted Jan. 21, 1975, to David T. Cass.
In operation, when the rear gripper assembly is positioned forwardly on the beam, the gripper shoes are hydraulically moved outwardly to gripping contact with the side walls of the tunnel. Then, the rotary cutterhead is rotated by drive motors while the thrust rams are simultaneously extended to thereby push the cutterhead and main frame, including the beam, longitudinally ahead. When the thrust rams reach their forward limits of travel, the rear gripper shoes are withdrawn from the tunnel wall and then the thrust cylinders are retracted to thereby draw the gripper assembly forwardly along the length of the beam into a new position. Thereafter, the rear gripper shoes are again moved outwardly into contact with the tunnel wall and the above procedure is repeated.
If the tunneling machine is to operate in relatively soft ground material, a forward gripper assembly, which is mounted on the main frame forwardly of the thrust rams, may be required to maintain the cutterhead and main frame in position while the rear gripper assembly is being repositioned. Similarly to the operation of the rear gripper assembly, the shoes of the front gripper assembly are hydraulically moved outwardly into gripping contact with the side wall of the tunnel. Thereafter, the thrust cylinders are retracted to pull the gripper assembly forwardly into a new position. Then the front gripper shoes are withdrawn while the rear gripper shoes are extended outwardly into contact with the tunnel wall to begin new boring sequence.
Various types of cutterheads have been commonly used in conjunction with the earth boring machine described above. The particular type of cutterhead with which this invention is concerned is termed an "open face" cutterhead and is characterized by openings in the face of the cutterhead to permit mined material to pass directly rearwardly through the cutterhead itself so that such material can then be carried out through the rear of the tunnel being bored.
An open face type of cutterhead having a typical arrangement of cutters is disclosed in U.S. Pat. No. 3,375,332, granted Sept. 4, 1973, to Clayton H. Crane, and assigned to The Robbins Company. This particular cutterhead includes a plurality of disc cutter assemblies positioned on the cutterhead for cutting concentric kerfs in the ground material. The disc cutters include circumferential cutting edges which are flanked by sloping breaker surfaces that serve to fracture and dislodge the rock material located between the kerfs which are cut by the cutting edges. A majority of the cutter assemblies are mounted on the front walls of radial spoke beams, which beams form part of the structure of the cutterhead. Other cutter assemblies are mounted on the front side of an auxiliary frame structure which is angularly offset from the radial spoke beams.
A second type of open face cutterhead is disclosed by the aforementioned publication of Carlo Grandori and by U.S. patent application Ser. No. 934,978 filed Aug. 18, 1978, by Carlo Grandori and assigned to The Robbins Company. This second type of open face rotary cutterhead includes a plurality of forwardly open, radially extending troughs. Roller cutters are mounted within the troughs to cut concentric kerfs upon rotation of the cutterhead. Segments which form breasting ring occupy the regions of the cutterhead between the radial troughs. The Grandori publication states that the rings support loose material against the tunnel face so that such material can be broken up into small enough pieces to thereby prevent damage to the tunneling machine. Accordingly, the ring segments are raised above the bottom of the trough to an elevation which permits the cutting edges of each cutter to project slightly forwardly of the ring segments. With reference to the direction of rotation of the cutterhead, the trailing end portion of each ring segment is fixedly attached to a shovel which forms the front wall of each radially extending trough. Fractured ground material theoretically passes rearwardly through the cutterhead through annular openings located between adjacent ring segments.
A disadvantage of this particular type of cutterhead stems from the fact that the "rings" are composed of segments and thus are not continuous. Pieces of rock which are too large to pass through the annular openings between the rings segments slides along the length of said openings until they abut against the shovel wall located at the terminal end portions of each ring segment. Thereupon, the large chunks of rock either damage the cutterhead as it continues to rotate or wedge so tightly between the front of the cutterhead and the face of the tunnel that the cutterhead is prevented from rotating, thus requiring the tunneling machine to be retracted so that such chunks of rock material can be manually broken up.
Furthermore, some of the individual ring segments in this second type of cutterhead are not of uniform width, but are wider near the terminal end portion of the ring segment; correspondingly, the annular openings are narrower in these areas. Thus, pieces of fractured rock which slide along the annular openings become wedged between the ring segments and are thereby prevented from freely passing rearwardly through the cutterhead.
A third type of open face cutterhead is disclosed by the aforementioned co-pending U.S. patent application Ser. No. 931,384. This particular cutterhead, which was developed in order to complete the subject invention, includes a plurality of radial spoke beams which are interconnected between a box-like hub structure and an annular box beam. Each radial spoke beam is constructed of a pair spaced apart side plate members. Mounts for mounting roller cutters on the cutterhead are receivable between and integrally connected to the side plate members to thereby also function as structural braces for the radial spoke beams. The cutterhead frame and the roller cutter mounts are configured to permit installation and removal of the roller cutters from the rear side of the cutterhead. The cutterhead also includes radially elongate scoops for collecting the fractured material and depositing it on a conveyor for removal rearwardly through the tunnel.
The above described patents together with the prior that was cited and considered by the Patent Office before granting them, and which is listed on the patents, along with the other prior art disclosed above, should be consulted for the purpose of properly evaluating the subject invention and putting it into proper prospective relative to the prior art.